1. Field of the Invention
The present invention generally relates to duplex printers. More particularly, it relates to sheet registration apparatus of duplex printers.
2. Prior Art
Duplex printing capabilities are fast becoming standard features in desktop printers. In duplex printing operations, a sheet of print media such as paper is: (1) drawn from a stack of sheets that are in registration, (2) sent to a printing device (electrophotographic printer or inkjet printer)where it receives printing on a first side of the sheet, (3) turned or xe2x80x9cflippedxe2x80x9d over and (4) sent back to the printing device where it receives printing on its second side. A sheet that has been flipped over will normally be out of registration with other sheets (that have likewise been flipped over) when said sheets are delivered to a common collection station. That is to say that these sheets experience lateral movements and/or skew movements with respect to each other as a result of being flipped over and otherwise handled by those sheet handling devices that are employed in duplex printers.
Consequently, sheets that have received printing on their first sides must be sent to a sheet registration device before they are sent back to the printer to receive printing on their second sides. In effect, the registration device physically eliminates the effects of the lateral and/or skew movements of the individual sheets and/or electronically compensates for the effects of such movements. Thus, high quality desktop duplex printing machines requirexe2x80x94and are commonly provided withxe2x80x94some kind of sheet registration device. The hereindescribed invention takes advantage of this circumstance.
The present invention provides sheet registration utilization devices that take further advantage of the sheet registration capabilities of printers in general and desktop duplex printers in particular. In effect, applicants sheet registration utilization devices perform additional operations on a stack of sheets that have been placed in registration by a registration device whose primary function is to place a stack of sheets in registration so that they can properly receive printing on their respective second sides. Thus, using the hereindescribed sheet registration devices, sheets registered in a duplex printer in order to print on their second sides are thereafter registered once more, so that a registered stack of such sheets can be bound (e.g., by gluing, stapling, etc.), provided with holes (e.g., for 3 hole punch systems, 2 hole punch systems, binder coil holes, etc.) or otherwise prepared for assembly.
The sheet registration utilization devices of this patent disclosure can be used with any automated business machine for producing or reproducing hard copy documents (such as electrophotographic printers, inkjet printers, copiers, facsimile machines, document scanners and the like) provided that such an automated business machine has a sheet registration mechanism. A wide variety of such sheet registration mechanisms are well known to the automated business machine manufacturing arts. Those sheet registration mechanisms that leave an edge side of a registered stack freely accessible to applicant""s sheet registration utilization device are, however, particularly preferred for practice of this invention.
Applicant""s sheet registration utilization devices are particularly useful in electrophotographic printers having duplex printing capabilities. Consequently, such a printer will be used as an example to further illustrate this invention. Such an electrophotographic printer apparatus could, for example, comprise: (1) a laser device for creating an image on a photoconductor drum, (2) a toner hopper for storing, and then dispensing toner particles on to the photoconductor drum, (3) a first sheet transport system that leads from a sheet dispenser tray to the printer device and then to an internal sheet registration device (such as a sheet collection tray which performs a registration function as part of a duplex printing function), (4) a second sheet transport system that carries a sheet from the internal sheet registration device back to the printer and (5) a sheet registration utilization device that takes further advantage of the sheet registration capability of the printer. For example, a sheet that has received printing on its second side can be sent back to the same registration device where it is again put in registration with a stack of other sheets. The resulting, twice registered, stack of duplex printed material is then subjected to an additional operation (e.g., stapling, gluing, hole punching, etc.) that requires that the sheets in the stack be in registration.